Objectives* 1. The reliability and applicability of a new, extremely sensitive and specific bioassay for tocopherol (vitamin E) will be increased by: a) determining the conditions which modify the response to tocopherol so that the assay can be more rigorously standardized; b) determining the variance in the results of replicate assays; and c) testing the ability of the assay to detect tocopherol in lipid mixtures. Complete methodological and statistical procedures for conducting this bioassay will be developed and described. 2. The role of vitamin E in the fertility of female and male rotifers will be determined by using tocopherol-deficient diets. 3. The dramatic influence of tocopherol on the development of females of the rotifer Asplanchna will be analyzed by examining the ultrastructure and nuclear numbers, volumes, and DNA contents of different tissues and organs in the small saccate and the much larger, tocopherol-induced, cruciform and campanulate morphotypes. These observations will document and may partially explain the processes by which tocopherol induces gigantism. 4. An unknown probably new vitamin E compound, present in plants both after cutting and senescence, will be purified and identified. The relative biopotency of this compound will be determined in the rat gestation-resorption assay, and information on the derivation and stability of the compound will be obtained.